First question is NO it not expensive to have a electric hook up when camping starting from only £29.99 for your hook up.
Here at Newquay Camping and leisure we sell a few different types of electric hook, the RCD Model, which I mentioned above, this is a weather proof unit with a trip box, like you would have in your home, from a few different manufacturers, we have the roller hook ups from Outwell which come in a variety of different designs, and the Crusader hook which come with 20m of cable and 3 sockets on it to plug your bits into.
What you can use on your electric hook up:
TV
Kettle (low wattage)
Phone charger
Hair Straighteners